AP BIOLOGY

Detailed explanation-1: -Therefore, 23 tetrads form during meiosis. During prophase I of meiosis I, the condensed homologous chromosomes line up to create tetrads, which are composed of two pairs of sister chromatids. Each homologous pair signs up with the help of proteins, and together they form what is called the synaptonemal complex.

Detailed explanation-2: -In plant-A, 2n= 12, n= gametic chromosome number. This means the number of chromosomes in a gamete of plant A is 6 and gametes will fuse to form a diploid organism having 12 chromosomes in each cell.

Detailed explanation-3: -Each pair of chromosomes-called a tetrad, or a bivalent-consists of four chromatids. At this point, the homologous chromosomes exchange genetic material by the process of crossing over (see linkage group).

Detailed explanation-4: -So if a cell has 12 chromosomes at the end of meiosis I which is reduction division, it means that the parent cell would have had 24 chromosomes in prophase I. At the end of meiosis II (which is similar to mitosis and hence, equational division occurs) it would have 12 chromosomes.

Detailed explanation-5: -Given that two chromosomes make up one bivalent and that the cell is in the diploid state (2n) and possesses 18 chromosomes, the number 18 will equal 9 when divided by 2. As a result, the cell’s 18 chromosomes will divide into 9 bivalents.